Mario writes: To show the basic principal I used a remote wall socket which normally is switched with a remote via a radio frequency of 433 MHz. What I wanted was to have an Arduino controlling the remote switch to turn on/off the wall socket.

Mario started with a commercial remote wall socket normally operated by RF, and hacked it by replacing the RF controller with a 4N35 optocoupler to open and close the switch.

All that was left to do was to write an Arduino sketch that listens to the Serial port for incoming data to switch the circuit, a small desktop program which transmits the control data, and as a bonus a small Android app which sends the switching state to the desktop program. To prepare your device/remote for being switched externally, you first have to desolder the buttons. In my remote the circuit layout was pretty simple and I could desolder the buttons pretty easily.